I want to register script with sql injection protection

I want to register script with sql injection protection.

PHP Code:

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<?php
$username = trim($_POST['username']);
$password = trim($_POST['password']);

$link = mysql_connect('localhost', 'mysql_user', 'mysql_password');
if (!$link) {    
die('Could not connect: ' . mysql_error());
}
echo 'Connected successfully';

$db_selected = mysql_select_db('foo', $link);

if (!$db_selected) {    
die ('Can\'t use foo : ' . mysql_error());
}

$sql = sprintf(    "INSERT INTO users(username,password) VALUES('%s','%s')",     mysql_real_escape_string($username),    mysql_real_escape_string(md5($password)));

$res = mysql_query($sql, $link);

mysql_close($link);

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Hmm i think he ment one that is for MSSQL and not for MySql and even that Mysql is old use MySql(I)